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You are right, the pluses are obvious, low cost power, avoidance of CO2, not much foreign dependance except on friendly Australia. Its base load and stable.

The minuses include the Pu239 that comes out of Uranium fission reactions, it is nasty and as the greens remind us has 20k year half life, so even 100k years still leaves it hot and deadly poisonous.

But there is a really good alternative in Thorium in the Liquid Fluoride Thorium Reactor or LFTR (Lifter) named after the god of war Thor ironically. It was invented by the same guy that invented the current PWR reactor, Alvin Weinberg a nuclear chemist.

Pluses, 4* more Th232 than U238 and it burns almost 100% into lighter valuable elements. U238 only burns about 1-5% in the once through cycle so almost all the waste is in fact unspent U238 fuel mixed with deadly Pu239 and useless Pu240 and other waste that needs a complex future breeder reactor. That won't likely ever happen anywhere.

The Thorium LFTR produces no Pu (okay 10000 less) in the waste so it decays to background in 300 yrs and this can be exploited for rare earths and radio medical isotopes worth their weight in gold in just 5 years.

Thorium is very simple to process into stable fluoride salts, 1 ton of metal per year produces 1GW continuous power for 1M homes with 1 ton of simple waste with very short decays.

The LFTR is intrinsically safe, if it overheats it melts a safety plug and shuts down, no backup needed. It is the ultimate passive design and it also follows load.

With the efficiency gained, Thorium allows for 100 times the total energy capacity of Uranium, enough for 10B people for 10000 years. Uranium can only power the worlds richest countries with a hidden agenda for weapons Pu.

The LFTR is also an excellent way to dispose of the current stock of unspent fuels, it eats them in the process of burning Thorium, that is how we get rid of the Pu waste.

So why do we use Uranium, simple, the US, UK, France, Israel, Russia, China, NKorea and Iran want the Pu for weapons and Thorium was killed off by Nixon because it is totally useless for weapons.

In the case of thorium-based reactors, wasn't there also an issue with the production of extra neutrons, that are needed to keep the subcritical fission reaction going ? Or am I confusing with another reactor design ?

The liquid Th232 is fertile so it needs to be bred to Protactinium and then to U235 by adding a small starter source of slow thermal neutrons from a fissile material like U232, U235 or Pu239 which could come form weapons or power plant wastes. Or you could just use a neutron beam powered by protons hitting lead, an energy amplifier.

The loop gains is 2 or so but is self moderated back by the fluoride salt.

There is only a tiny amount of U235 in the loop at any time, it breeds itself as it follows the load slowly but surely consuming the Th232 and replacing it with the fission products of the self procreating U235. Just 1 ton of Th232 gives 3GW/yr thermal power and 1 ton of interesting waste, (almost 1 ton, remember e=mcc).

See Kirk Sorenson for the story.

In Fukushima the reactor did shut down properly, but had no extra water from the backup deisel to cool the reactor with, hence the chain of events.

The LFTR is completely self moderating for load and if it overheats it shuts down by melting its own bath plug. As it drains it cools in a few hours since it is always in liquid fluoride salt form. No emergency devices or computers or people or power needed. To restart, heat the bath tub/pan and start the pumps up. The heat from the tiny amount of U235 in the salt is exchanged with a steam or helium or CO2 turbine.

Modern passive Uranium designs like the AP1000 will copy some of the same ideas but really most active reactors are an accident waiting to happen with probability in the 1 in 1000..s of years per site unless they are passive by design. A few active reactors is safe, but 1000s of them is begging, so the next generation must all be passive by design and I'm sure they will be. Even better if the LFTR would replace the U235 cycle as it is maybe 100* more efficient with the fuel.

Also, another question about the LFTR reactor : even if it is subcritical, doesn't it have the same cooling problems that plagued some of Fukushima's reactors ?

IIRC, the problem with some reactors was that the core of the reactor remained hot while the flow of coolant was interrupted due to a power shortage, which caused the bottom of the reactor to melt and wastes to flow to someplace where they were not supposed to flow (the sea ?)

The story of nuclear power really starts when the larger stars go supernova, as the stellar core collapses there is one enormous neutron flux that converts some of the iron, nickel into fertile U238 and Th232 in just a few seconds. The sequence that follows is similar to what happens in current reactors.